Roof supports



May 26, 1959 A. W. DUNCAN ROOF SUPPORTS Filed June l5, 1953 flan! l l i4 42 50 53 55 3l INVENTOR. ANGUS W. DUNCAN United States Patent O ROOFSUPPORTS Angus Wellesley Duncan, Worcester, England, assignor to TheMining Engineering Company Limited, Worcester, England Application June15, 1953, serial No. 361,752 claims priority, application Great BritainJune 16, 1952 1 Claim. (c1. 24a- 354) This invention concernsimprovements in hydraulic roof supports of the kind employed in mines.

In props and other roof supports of the hydraulic type used in miningpractice, it is common to tit a relief valve to limit ythe load whichthe prop can carry and to permit the support to yield as the roofpressure exceeds the load which the prop is designed to carry.

When such relief valves operate there is a substantial drop in theresistance olered by the prop which is undesirable for good roof controland it has been proposed to use valves of low hysteresis characteristicsto reduce the drop in hydraulic pressure and thus to achieve, as far aspossible, a prop olering constant resistance to roof pressure. I

One object of the present invention is to provide a mine roof support ofthe hydraulic type having improved resistance characteristics.

Furthermore, with roof supports which are self-setting and preloading(such for example as those described in my co-pending application No.355,831) it may be, in certain circumstances, that the pressure exertedon the roof support by the convergence of the roof and oor does notreach the load at which the support is arranged to yield. Such acondition might obtain, for example, when the oor of the seam is so softthat the support penetrates the iloor at a load less than the yield loadof the prop.

In such circumstances, the hydraulic accumulator, if arranged to work upto.or nearly up to the full Working pressure of the support, may notstore a suicient volume of the working fluid to actuate the self-settingmotor and to preload the support in its next settingv position. Anotherobject of the invention is to provide a roof support in which it ispossible to store sucient pressure lluid in the accumulator to operate aself-setting motor and to preload the support to a proportion of therated loading even when the effective roof load acting on the support isless than the yield load.

From one aspect the invention provides an hydraulic roof supportcomprising a hollow ram constituting a uid reservoir operating in acylinder, a relief valve connecting the cylinder to the reservoir and ahydraulic accumulator connectible for charging from the main cylinderunderroof load.

The accumulator may have a working range yat least up to the pressure atwhich the relief valve operates whereby hysteresis losses in the valveare counteracted and resistance of the prop under bump roof conditionsis maintained.

In other forms, the accumulator is of limited capacity and has a workingrange substantially lower than the pressure at which the relief valveoperates so that the prop yields initially at the accumulator pressureup to the capacity of the accumulator and thereafter at ythe reliefvalve pressure.

From another aspect, the invention provides an hydraulic roof supportcomprising a hollow ram constituting a uid reservoir operating in acylinder to which cylinder fluid is transferred fromv the reservoir by apump to set the support and having a relief valve set to open at apredetermined pressure arranged between the reservoir and the cylinderand a hydraulic accumulator having a maximum working pressure at leastequal to the maxi; mum pressure in the system and a minimum pressureslightly below the ypressure at which the relief valve operates,connected to the cylinder so as to be chargeable thereby, so that on asudden increase in load on the support a proportion of theresultantpressure increase in the cylinder is absorbed in theaccumulator whereby the pressure change to which the relief valve issubjected is reduced. f`

A pressure 'sensitive valve may be arranged between the accumulator andthe main cylinder to close and isolate the accumulator when the pressureinthe system rises above the maximum pressure value of the accumulatorpressure range.

The accumulator'may be of the spring type, air piston type or air bagtype.

Other parts of the invention are embodied in the preferred form whichwill now be described in some detail with reference to the accompanyingdiagrammatic drawings in which Fig. l is a section through aself-setting preloading prop embodying an air bag type of accumulator;

Fig. 2 is a vertical section through the manually operable valveillustrating the accumulator charging position;

Fig. 3 is a vertical section similar to Fig. 2 illustrating the valve inposition to expand the cylinder work chamber with the stored energy inthe accumulator, and

Fig. 4 is a vertical section similar to Fig. 2 illustrating the valve inposition to isolate the accumulator.

The prop as shown in Fig. l is of the self-setting preloaded type ,inAwhich the energy stored in the accumulator by roof subsidence is used toset the prop and also to exert a preload on the roof. It comprises acylinder 20 in which a hollow ram 21 works with the ram and cylinderforming an expansible Work chamber 60 and the ram defining an oilreservoir 61 separated from the Work chamber by wall 62. A relief valve22 yconnects the cylinder to the interior of the reservoir 61 by apassage 63 formed in the wall 62.

A hydraulic accumulator 23 of the air bag type is iitted to the support.The accumulator 23 comprises a llexible bag 30 containing air underpressure. The bag is housed in a chamber 31 and its maximum extension isdetermined by a guard plate 32 having holes 33 therethrough so that oilcan pass through to exert pressure on the bag. A pressure sensitivevalve 34 is interposed in the passage 42 connecting the accumulator tothe manually operated valve and hence to the main cylinder Work chamber60. This accumulator can be selectively connected to the work chamber 60through ports in a manually operable valve 24 of the type shown in Figs.2, 3 and 4, so that: the accumulator may be charged when the prop iscom-J Fig. 2 shows the valve 24 pressed under roof pressure. in theaccumulator charging position in which the cylinder work chamber 60k isconnected to the accumulator so that the latter may be charged underroof pressure. After this occurs, valve 34 moves to the right as showinand isolates the accumulator. Port 41 in housing 40 of valve 24communicates with work chamber 60, and port 42 communicates with theaccumulator 31. In Fig. 2, port 41 is aligned with passage 43 in valve24, which is aligned with port 44 leading to pressure sensitive valve 34and thence to port 42. The space within cylinder 25 below piston 26 isin communication with the space above piston 26 by port 45, passage 47in valve 24, port48 and passage 49 in wall of cylinder 25.

The accumulator is connectible through the Ymanually Patented May 26,1959 operated valve 24 to exert pressure upon the upper surface of apiston 26 of an auxiliary cylinder 25 to raise the ram. The piston 26 isconnected by a hollow rod 27 yto a larger piston 28 working in thereservoir. Pressure on the piston 26 thus puts pressure upon the fluidin the reservoir to transfer it to the main cylinder for the setting ofthe prop through the hollow rod 27 which communicates with the reservoirthrough a port 29 in a manner to be explained below. Fig. 3 shows thevalve in position to raise the ram 21. In this position, passage 55 fromaccumulator 31 is aligned with passage 56 through valve Z4 and thispassage 56 is aligned with port 48 leading to passage 49, in the wall ofthe cylinder. The space above piston 26 is thus put into communicationwith the oil under pressure in the accumulator and piston 26 movesdownwardly bringing with it piston 28 and exerting pressure on the fluidin reservoir 61. Fluid then passes through port 29 down pipe 27 intocylinder 25 below the piston 26 and thence through port 45, passage 47in valve 24 and port 57 into work chamber 60. The fluid pressure thusadmitted to the work chamber then exerts force against the lower surfaceof wall 62 and on an additional surface 65, which moves the ram upwardlyto extend the prop against the roof. When the prop is to be extended, itis obvious that the prop is initially collapsed and there is no pressurein work chamber 60.

The manually operable valve 24 can be set to isolate the accumulatorfrom the cylinder as shown in Fig. 4. In this position, the accumulator31 is isolated and main work chamber 60 is connected to the auxiliarycylinder 25 below piston 26 and thus to the reservoir 61 through port57, passage 47, po-rt 45, rod 27 and port 29.

In operation, after the prop is initially set in position, valve 24 isset as shown in Fig. 2. The pressure sensitive valve 34 is biased intothe position shown in Fig. l by spring 50. One end of valve 34communicates with cylinder 25 through port 51, groove 52 around valve 24and port 53, and the other end communicates with work chamber 60 throughport 54 forming an extension of port 44. If, with valve 24 in theposition shown in Fig. l, roof pressure forces ram 21 downwardly, thepressure below ram 21 increases, and so does the pressure in theaccumulator 31. Valve 34 moves to the right, as shown in Fig. 2, closingthe accumulator oi from the work chamber 60. Thereafter, pressure withinthe work chamber 60 can rise due to further depression of the ram 21until relief valve 22 operates to allow oil to pass from beneath workchamber 60 to the oil reservoir within ram 21. Then when the support isto be moved, valve 24 is set into the position of Fig. 4 to lower theram. When the ram is to be raised, valve 24 is set in the position shownin Fig. 3. With the valve 24 in this position pressure from theaccumulator follows a path through passage 55, passage 56, port 48,passage 49 to act on the upper surface of piston 26 and urge itdownwardly. This creates a pressure `in reservoir 61 because piston 2Sis also urged downwardly by rod 27. Fluid in the reservoir 61 is forcedto ow through port 29 and rod 27, through cylinder 25, port 45,V passage47, and port 57 to create a pressure in work chamber 60. Since workchamber 60 and reservoir 61 are now in free communication, theirpressures are equal. But, the pressure in work chamber 60 also acts onannular pressure surface and the ram is moved upwardly.

It is thus possible to store sufficient pressure fluid in theaccumulator to operate a self-setting motor and yto preload the supportto a propoltion of the rated loading even when the effective roof loadacting on the support is less than the yield load.

It will be understood that, Where the hydraulic accumulator is of theair bag or similar type, it is a relatively simple matter to adjust itsworking range and, with an adjustable pressure sensitive valve, theroolf support can be adjusted to operate in practically all conditionslikely to be encountered in mining practice.

Such adjustment of both accumulator and pressure sensitive valve may heaccomplished after dismantling the support, or external means such asvthe screw threaded plug 36 may be provided to make the adjustmentwithout having `to dismantle.

It will be understood that the invention is not restricted to thedetails of the preferred forms which may be modified without departingfrom the broad ideas underlying them and dened in the accompanyingclaim.

I claim:

A hydraulic roof support comprising a housing having` a main cylinder, aram operating in said cylinder and forming therewith an expansible workchamber, said ram being hollow and forming a separate fluid reservoir, ahydraulically loaded accumulator in said housing, said housing having afluid communication passage between said cylinder work chamber andl saidaccumulator and through which the accumulator may be charged from thework chamber under roof load, said ram having a fluid communicationpassage between said cylinder work chamber and said reservoir, anonreturn relief valve controlling said ram passage and operable to passfluid from the cylinder work chamber to the reservoir, and a pressuresensitive valve controlling said passage between the accumulator and themain cylinder work chamber, said relief valve having an operating valueat lease as great as the operating value of said pressure sensitivevalve for controlling the working pressure-range of the accumulatorrelative to the pressure in the cylinder work chamber.

References Citedl in the le of this patent UNITED STATES PATENTS1,510,462 Dell Oct. 7, 1924 1,812,577 Albertine Iunev30, 193.1 1,976,129Johnson Oct. 9, 1934 2,555,427 Trautman June 5, 1951 2,584,820 SteinholFeb. 5, 1952 2,597,050 Audemar May 20, 1952 2,621,631 Dowty Dec. 16,1952 2,752,757 Joy July 3, 1956 FOREIGN PATENTS 493,811 Belgium Feb.281950 1,016,105 France Aug. 20, 1952 608,054 Great Britain Sept; 91948`

